Pope Benedict III (Latin: Benedictus III) was Pope from 29 September 855 to his death in 858.

Little is known of Benedict's life before his papacy. His father was Peter. He was educated and lived in Rome and was cardinal priest of the church of San Callisto at the time of his election. Benedict had a reputation for learning and piety. He was elected upon the refusal of Hadrian, the initial choice of the clergy and people. A group of important people preferred a different candidate, Anastasius. This latter group had Benedict's election disavowed and Anastasius installed. However, popular opinion was so strong that Benedict's consecration was allowed. The envoys of Holy Roman Emperor Louis II forced Benedict to handle Anastasius and his adherents leniently. The schism helped to weaken the hold of the emperors upon the popes, especially upon their elections.

Benedict intervened in the conflict between the sons of Lothair I (the future King Lothair II of Lotharingia, Emperor Louis II and Charles of Provence) on the latter's death. He was active in other cases as well and adopted a firm position towards Constantinople.

Æthelwulf of Wessex and his son, the future king Alfred the Great, visited Rome in Benedict's reign. The Schola Anglorum, which was destroyed by fire in 847, was restored by Benedict.